Cryptology ePrint Archive: Report 2005/292

Improved Integral Cryptanalysis of FOX Block Cipher

Wu Wenling, Zhang Wentao, and Feng Dengguo

Abstract: FOX is a new family of block ciphers presented recently, which is based upon some results on proven security and has high performances on various platforms. In this paper, we construct some distinguishers between 3-round FOX and a random permutation of the blocks space. By using integral attack and collision-searching techniques, the distinguishers are used to attack on 4, 5, 6 and 7-round of FOX64, 4 and 5-round FOX128. The attack is more efficient than previous integral attack on FOX. The complexity of improved integral attack is $2^{77.6}$ on 4-round FOX128, $2^{205.6}$ against 5-round FOX128 respectively. For FOX64, the complexity of improved integral attack is $2^{45.4}$ on 4-round FOX64, $2^{109.4}$ against 5-round FOX64, $2^{173.4}$ against 6-round FOX64, $2^{237.4}$ against 7-round FOX64 respectively. Therefore, 4-round FOX64/64, 5-round FOX64/128, 6-round FOX64/192, 7-round FOX64/256 and 5-round FOX128/256 are not immune to the attack in this paper.

Category / Keywords: secret-key cryptography / Block cipher; FOX; Integral Cryptanalysis.

Date: received 25 Aug 2005

Contact author: wwl at is iscas ac cn

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Version: 20050901:064610 (All versions of this report)

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